[PATCH] tty: Fix data race between tiocsti() and flush_to_ldisc()
gregkh at linuxfoundation.org
Fri Aug 13 07:33:29 UTC 2021
On Sun, Aug 08, 2021 at 03:05:13AM +0800, Nguyen Dinh Phi wrote:
> The ops->receive_buf() may be accessed concurrently from these two
> functions. If the driver flushes data to the line discipline
> receive_buf() method while tiocsti() is using the ops->receive_buf(),
> the data race will happen.
> For example:
> tty_ioctl |tty_ldisc_receive_buf
> ->tioctsi | ->tty_port_default_receive_buf
> | ->tty_ldisc_receive_buf
> ->hci_uart_tty_receive | ->hci_uart_tty_receive
> ->h4_recv | ->h4_recv
> In this case, the h4 receive buffer will be overwritten by the
> latecomer, and it cause a memory leak.
That looks to be a bug in the h4 code, if the receive_buf() call can not
be run at the same time, it should have a lock in it, right?
> Hence, change tioctsi() function to use the exclusive lock interface
> from tty_buffer to avoid the data race.
Where is the lock being grabbed from the other receive_buf() call path
to ensure that the lock is always needed here?
> Signed-off-by: Nguyen Dinh Phi <phind.uet at gmail.com>
> Reported-by: syzbot+97388eb9d31b997fe1d0 at syzkaller.appspotmail.com
> drivers/tty/tty_io.c | 2 ++
> 1 file changed, 2 insertions(+)
> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> index e8532006e960..746fe13a2054 100644
> --- a/drivers/tty/tty_io.c
> +++ b/drivers/tty/tty_io.c
> @@ -2307,8 +2307,10 @@ static int tiocsti(struct tty_struct *tty, char __user *p)
> ld = tty_ldisc_ref_wait(tty);
> if (!ld)
> return -EIO;
> + tty_buffer_lock_exclusive(tty->port);
> if (ld->ops->receive_buf)
> ld->ops->receive_buf(tty, &ch, &mbz, 1);
> + tty_buffer_unlock_exclusive(tty->port);
Did this fix the syzbot reported issue?
More information about the Linux-kernel-mentees